The offeror plans to optimize a microplaque assay which is newly developed in his laboratory. This assay will permit development of a quantitative neutralizing antibody assay. The enumerative assay is based on direct plaque reduction after treatment of viral inocula with serum containing neutralizing antibody against HIV 1. The new assay will be compared to inhibition of reverse transcriptase, and inhibition of thymidine uptake, as well as plaque reduction in poly-L-lysine attached monolayers. The effects of genetic diversity will be assayed by measuring the effect of ten well characterized neutralizing reference sera against 40 relatively stable HIV 1 isolates from geographically diverse sources. To determine which sub-component of the virus elicits neutralizing antibody, experimental animals (mice, rabbits and guinea pigs) will be inoculated using electrophoretically purified sub-components, as well as recombinant sub-components. The same electrophoretically purified proteins will be transferred to nitrocellulose and used to absorb reference human antisera. The recombinant sub-components will be bound to polystyrene beads and then used to absorb the reference human antisera.